Abstract: The sliding mode variable structure control method was introduced with the horizontal regulator as an example. Under the precondition of the optimization of performance criterion, the computation of the switch function was accomplished; and the unit vector method was adopted to realize a completely new design method for gun control system. The controller designed with this method contains only one switch function. Furthermore, the switch function was easy to be continuously approximated. The simulation results based on MATLAB conditions were satisfying. The results showed that if unit regulator was used, the accuracy was 33 times higher than the specification, and 233 times higher than that of the traditional method. This design method is suitable to design of autopilots of missiles and other aircraft as well.